ES2884792T3 - Brazing alloy - Google Patents

Abstract

A bar solder, having an alloy composition comprising, by mass %, 0.8% to 10% Cu, 0.03% to 0.4% Ni, optionally, at least one of 0 .3% or less of P, 0.3% or less of Ge and 0.3% or less of Ga, optionally, at least one selected from at least one group of a group consisting of at least one of In , Sb, Zn and Ag in a total amount of 5% or less, and a group consisting of at least one of Mn, Cr, Co, Fe, Si, Al, Ti and rare earth elements in a total amount of 1 % or less, the remainder being Sn and including an intermetallic compound, wherein the intermetallic compound has a maximum grain size of 100 μm or less in a region at least 50 μm from a surface of the bar weld, wherein the Intermetallic compound is mainly (Cu, Ni)6Sn5.

Description

DESCRIPTION

solder alloy

technical field

The present invention relates to a brazing alloy excellent in continuous castability and a brazing joint including the brazing alloy.

prior art

Electronic components are mounted on printed circuit boards. Examples of the electronic component assembly step include flow soldering, dip soldering, and the like. Flow soldering is a method in which soldering is performed by applying a jet flow from a solder pool to one side of the connection surface of the printed circuit board. Dip soldering is a method in which a terminal, such as a coil component, is immersed in a solder bath to remove an insulating film and perform metal plating prior to soldering.

For flow or dip soldering, a solder bath is required. Since the weld pool is exposed to the atmosphere for a long time, the slag generated in the weld pool must be removed at regular intervals. Also, the molten solder from the solder pool is consumed when soldering. Therefore, the brazing alloy is periodically supplied to the brazing pool. For the supply of the solder alloy, a solder bar is generally used.

As a method of manufacturing a bar weldment, there are a method of pouring the molten weld into a fixed mold and a continuous casting method in which the molten weld is poured into a rotating mold. The continuous casting method is a method in which a raw material is placed in a melting furnace and melted, and the solder molten in the melting furnace is cast into a slot in a rotary mold. Examples of the mold used in the continuous casting method include a mold having a shape in which a groove is provided at a center portion in a widthwise direction of the annular plate. The molten solder solidifies after being cast into the rotary mold slot and is guided from the mold to the cutting stage at a temperature of approximately 150°C. The guided continuous cast product is cut to a predetermined length to form a bar weld.

A technique for continuous casting of a brazing alloy is disclosed in, for example, Patent Document 1. This reference discloses that a cooling metal through which cooling water flows is placed in direct contact with the outside of the mold. , the cooling rate to 280 °C is 3 °C/s or higher, preferably 20 °C/s or higher, and more preferably 50 °C/s or higher, and the structure of the eutectic part is refined, in the alloy Au-Sn based solder. However, although Au is sometimes used as a high-temperature Pb-free brazing alloy, Au is expensive and difficult to process.

Therefore, for bar brazing, Sn-Cu based brazing alloy is mainly used. It is common for Sn-Cu based brazing alloy to form intermetallic compounds in brazing alloys. When the alloy is made by a continuous casting method, a coarse, brittle intermetallic compound can be generated during solidification of the molten solder. When the coarse intermetallic compound is generated, the brazing alloy may crack at the generation site, which may cause a problem that a continuous casting product cannot be formed. Additionally, even when a continuous cast product can be formed, there is a risk of breakage during transportation.

As an example of the study of the Sn-Cu-based brazing alloy, from the point of view of preventing the breakage of the joint formed by the brazing alloy, for example, Patent Document 2 describes that an alloy based on Sn-Cu is used. Sn-Cu-Ni base as a low-temperature brazing material, a flux is applied to the joint site of a pipe, the alloy is dipped into a brazing filler metal, and then cooled and solidified slowly.

Patent literature 3 discloses a solder ball that is formed by an Sn-Bi type alloy containing Sn as the main element, 0.3 to 2.0% by mass of Cu, 0.01 to 0.2 % by mass of Ni and 0.1 to 3.0 % by mass of Bi, and an intermetallic compound of (Cu, Ni) ⁶ Sn ^{5 is formed} in the Sn-Bi alloy so that the generation of gaps in the junction when bonded to an electrode, a thermal fatigue property is excellent, and a good drop impact resistance property can also be obtained.

citation list

Patent bibliography

Patent Document 1: JP 2017-196647 A

Patent document 2: WO 2014/084242 A1

Patent document 3: US 2015/146394 A1

Non-patent literature

Non-Patent Document 1: Yasutaka Hashimoto et al., "Current Status and Future Plan of Viscosity Measurement for the Lead-Free Solder," Journal of the Japan Institute of Metals and Materials, J-STAGE Early Review Published, March 27 of 2017

Summary of the invention

technical problem

The object of the invention described in Patent Document 2 is to provide an alloy that is easy to use at a low melting point and allows the Cu content to be in the range of 0.3% to 41.4%. However, as described in the patent literature, since the temperature of the liquid at 41.4% Cu content is 640 °C, and the alloy cools and solidifies slowly, the coarse intermetallic compound precipitates into the alloy layer. Therefore, when the continuous cast product is made using the Sn-Cu base alloy described in Patent Document 2, cracks or breakage may occur in the continuous cast product. When cracking or breakage occurs in the continuous casting product, the continuous casting process is interrupted, and the casting process is restarted after removal of the broken cast product from the mold, thus the operation process is complicated.

Furthermore, in recent years, it is desired to manufacture a longer continuous cast product, since cost reduction due to process labor and process duration reduction must always be pursued. Therefore, breakage of the continuous cast product during continuous casting is considered a bigger problem than ever.

Additionally, the viscosity of the molten solder varies greatly depending on the composition of the alloy, and depending on the composition, the molten solder is less likely to flow into the grooves of the rotary mold. For this reason, since the continuous cast product thickens, the coarse intermetallic compound may be generated even when the mold is very cold, causing the continuous cast product to break. Therefore, even when the Sn-Cu-based alloy described in Patent Document 2 is applied to Patent Document 1, breakage of the continuous cast product may occur.

An object of the present invention is to provide a brazing alloy excellent in continuous castability.

Solution to the problem

The present inventors have further studied the problem generated in the case of manufacturing the alloy described in Patent Document 2 as a continuous cast product. In Patent Document 2, it is intended to prevent cracking of the brazing alloy by slowly cooling the brazing material during joining. For example, when slow cooling is performed as described in Patent Document 2, the coarse intermetallic compound is generated within the brazing alloy. At the site where the coarse intermetallic compound is generated, cracking occurs during solidification or breakage occurs when the brazing alloy is cut. This is particularly noticeable in a hypereutectic alloy where the Cu content is 0.8% or more.

Therefore, the present inventors focused on cooling during continuous casting product manufacturing, instead of focusing on cooling during bonding as described in Patent Document 2. Specifically, in continuous casting using Sn-Cu brazing alloy with Cu content equal to or greater than 0.8%, it was confirmed that the intermetallic compound generated within the brazing alloy was coarse when casting while cooling the mold as described in Patent Document 1. Furthermore, Non-Patent Document 1 reports that the viscosity of the molten solder increases as the Cu content increases. It has been reported in the paper that when the Cu content was increased from 0.7% to 7.6%, the viscosity at the same temperature was increased by about 1.5 times. Therefore, when casting with different Cu contents, it was found that the fluidity of the molten solder in the mold decreased as Cu content increased, and the frequency of crack occurrence during solidification also increased as Cu content increased. which increased the thickness of the plate.

To compensate for a decrease in fluidity of the molten solder due to an increase in Cu content, it is possible to tilt the rotary mold so that the cast molten solder flows downstream from upstream. However, when the rotary mold is tilted, the cross-sectional shape of the cast product is very different from the shape of the groove of the mold, so that a desired cast product cannot be obtained. On the other hand, when the tilt angle of the rotary mold is too large, the molten solder may protrude from the groove when the molten solder flows through the curved part of the rotary mold. Therefore, in In case of using the continuous casting method, the rotary mold should keep the horizontal state.

The present inventors have further studied a molten solder such that the molten solder flows sufficiently in the mold to prevent cracking or breakage during solidification even when the molten solder having a high-viscosity alloy composition is cast into a mold. in a state that the rotary mold maintains the horizontal state. Although cracking or breakage of the continuous cast product has been conventionally considered to be induced by the vibration of the rotary mold, it is found that, when micro-vibration such as ultrasonic waves are applied to the molten solder cast in the mold, the fluidity of the molten solder in the mold unexpectedly improves and the maximum grain size of the intermetallic compound unexpectedly decreases. As a result, a continuous cast product having good quality without cracking and breaking during solidification can be manufactured, and the present invention has been achieved.

The present invention is defined in the claims.

Brief description of the drawings

[FIG. 1] FIG. 1 is a cross-sectional view of a solder alloy from Example 7.

[FIG. 2] FIG. 2 is a cross-sectional view of the solder alloys of Example 8 and Comparative Example 4, with FIG. 2(a) the image of Example 8 and FIG. 2(b) the image of Comparative Example 4.

Description of achievements

The present invention is described in detail below. In the description, "%" referring to a solder alloy composition is "% by mass", unless otherwise specified.

1. Alloy composition of a solder alloy:

(1) Cu: 0.8% to 10%

The brazing alloy of the present invention can solve the problem encountered in the case of a hypereutectic alloy in which a thick CuSn intermetallic compound is likely to be generated. When the Cu content is less than 0.7%, a hypoeutectic alloy is produced, so that the primary crystal during solidification is Sn, when the Cu content exceeds 0.7%, a hypereutectic alloy is produced, so so that the primary crystal during solidification is a SnCu compound. When the primary crystal is a SnCu compound, the fluidity of the molten solder in the mold deteriorates. However, when the Cu content is slightly higher than 0.7%, there is little influence of the intermetallic compound during casting, regardless of the manufacturing conditions. Since the effect of the present invention is more likely to be manifested as the Cu content is higher, in terms of the lower limit, the Cu content is 0.8% or higher, preferably 1.0% or greater, and more preferably 4.0% or greater.

When the Cu content exceeds 10%, the temperature of the liquid is high, which deteriorates the workability. When the Cu content exceeds 10%, the area ratio of the intermetallic compound is too high. In addition, since the viscosity of the molten solder increases and the fluidity in the mold deteriorates, the coarse intermetallic compound is generated. As a result, cracking or the like occurs during solidification. In terms of the upper limit, the Cu content is 10% or less, preferably 8% or less, and more preferably 7% or less.

(2) Ni: 0.03% to 0.4%

Ni is an element capable of controlling the grain size of the intermetallic compound SnCu. Sn-Cu brazing alloy contains Ni, and Ni can be uniformly dispersed in Cu ⁶ Sn ⁵ to make the grain size of the intermetallic compound finer and prevent breakage of the continuous casting product. When the Ni content is 0.4% or less, a rise in liquid temperature is within an allowable range, and therefore good workability can be maintained. In terms of the upper limit, the Ni content is preferably 0.2% or less, and more preferably 0.15% or less. On the other hand, to achieve the effect based on Ni incorporation, in terms of the lower limit, the Ni content is 0.03% or more, and preferably 0.1% or more.

Ni is contained and the intermetallic compound of the present invention is mainly (Cu, Ni) ⁶ Sn ⁵ . The expression "mainly (Cu, Ni) ⁶ Sn ⁵ " means that the ratio of the area of (Cu, Ni) ⁶ Sn ⁵ to the total area of the intermetallic compound is 0.5 or more when the cross section of the solder alloy.

(3) At least one of P: 0.3% or less, Ge: 0.3% or less, and Ga: 0.3% or less

These elements are optional elements capable of preventing the oxidation of the solder alloy and improving the fluidity of molten solder. In terms of the upper limit, when the content is 0.3 % or less, the temperature rise of the liquid can be prevented, so that the time to solidification can be shortened, and the oiling of the liquid structure can be prevented. the alloy. In terms of the upper limit, the content of P is 0.3% or less, more preferably 0.1% or less, and more preferably 0.025% or less. In terms of the upper limit, the Ge content and the Ga content are 0.3% or less, respectively, and more preferably 0.15% or less, respectively. On the other hand, to achieve the effect based on the incorporation of these elements, in terms of the lower limit, the content of each element is preferably 0.005% or more, and more preferably 0.01% or more.

(4) At least one selected from at least one group from a group consisting of at least one of In, Sb, Zn, and Ag in a total amount of 5% or less, and a group consisting of Mn, Cr, Co , Fe, Si, Al, Ti and rare earth elements in a total amount of 1% or less

With respect to these elements, as long as the total amount of at least one of In, Sb, Zn and Ag is 5% or less, and the total amount of at least one of Mn, Cr, Co, Fe, Si, Al , Ti and rare earth elements is 1% or less, the continuous castability of the brazing alloy in the present invention is not affected. In the present invention, the term "rare earth elements" refers to 17 types of elements, which are Sc and Y belonging to Group 3 and 15 elements of the lanthanum group corresponding to atomic numbers 57 to 71 of the periodic table.

In the present invention, at least one of In, Sb, Zn, Ag, Mn, Cr, Co, Fe, Si, Al, Ti and rare earths can be included. As for the content of each element, the total amount of at least one of In, Sb, Zn and Ag is 5% or less, and the total amount of at least one of Mn, Cr, Co, Fe, Si, Al , Ti and rare earth elements is 1% or less. The total amount of at least one of In, Sb, Zn and Ag is more preferably 1% or less, and the total amount of at least one of Mn, Cr, Co, Fe, Si, Al, Ti and earth elements rare is more preferably 0.5% or less.

(5) Rest: Sn

The remainder of the brazing alloy of the present invention is Sn. In addition to the above items, there may be unavoidable impurities. Even if unavoidable impurities are contained, the effects described above are not affected. Furthermore, as described below, even when an element not contained in the present invention is contained as an unavoidable impurity, the effect described above is not affected.

(6) Alloy structure

In the brazing alloy of the present invention, the maximum grain size of the intermetallic compound is 100 µm or less in a region at least 50 µm from the surface of the brazing alloy.

Regarding the Sn-Cu brazing alloy, in the related art, since only the grain size of the bonding interface between the brazing alloy and the electrode was focused on, there was no report on the size. grain of the cast product itself before joining. Furthermore, in the study of the conventional bonding interface, since it was necessary to set the manufacturing conditions taking into account the influence on the substrate, electronic component or the like to be bonded, the speed of bonding could not be increased. cooling.

On the other hand, in the present invention, the continuous casting problem can be solved for the first time by intentionally focusing on the structure of the Sn-Cu solder alloy before the solder joint, which is a continuous casting product. manufactured by continuous casting.

The molten solder cools from the mold contact surface and the central part farthest from the mold contact surface eventually solidifies. This is because the cooling rate at the mold contact surface is faster than the cooling rate at the center. The faster the cooling rate, the smaller the grain size. Therefore, generally, the surface of the cooled cast product in the mold is finer than the central part.

However, breakage during continuous casting cannot be prevented even when only the vicinity of the surface of the brazing alloy has a fine structure. In addition, when a large amount of the intermetallic compound, which is brittle and coarse, is generated during solidification, the bulk of the brazing alloy cannot be formed. When there is such an intermetallic compound inside, a large crack is generated inside, and therefore, there is a risk that the continuous casting product will break at a stage after continuous casting even when the crack does not appear on the surface. surface due to the fine structure in the vicinity of the surface and the break cannot be recognized by its appearance. Furthermore, even when the average grain size inside the brazing alloy is defined, the existence of a coarse intermetallic compound leads to cracking of the brazing alloy. Therefore, in the present invention, the maximum grain size inside the brazing alloy is defined, and the maximum grain size is small, to prevent breakage during continuous casting.

The maximum grain size in the present invention is defined as follows. An image is seen in Cross-section of a cast product to identify an intermetallic compound, selecting the largest grain by eye. Two lines parallel to each other are drawn for grains to maximize an interval, and the interval is defined as the maximum grain size.

The smaller the maximum grain size, the better the continuous castability. Therefore, in terms of the upper limit, the maximum grain size is 100 pm or less, preferably 80 pm or less, more preferably 60.44 pm or less, furthermore more preferably 58.50 pm or less, and even more preferably 50 pm or less.

The intermetallic compound is generated based on the constituent elements. In the present invention, the intermetallic compound caused by the alloy composition containing Sn, Cu and Ni is mainly (Cu, Ni)aSn ⁵ as described above.

In the present invention, the area ratio of the intermetallic compound in the brazing alloy is preferably 40% or less, more preferably 30% or less, even more preferably 20% or less, particularly preferably 18.06%. or less, and most preferably 15.15 mm or less from the viewpoint of reducing the amount of precipitation of the brittle intermetallic compound and preventing breakage.

Also, in the Sn-Cu brazing alloy, when the intermetallic compound has a small grain size and the precipitation amount of the brittle intermetallic compound is small, cracking can be further prevented. In the brazing alloy of the present invention, the following relationship (1) is preferably satisfied in consideration of the balance between them.

Maximum grain size (pm) * area ratio (%) of intermetallic compound of the brazing alloy < 3000 (pm%)....(1)

The "ratio of the area of the intermetallic compound in the braze alloy" represents the ratio (%) of the area of the intermetallic compound existing on the cut surface to the area of the cut surface obtained by cutting the braze alloy. The right part of the above relation (1) is more preferably a % of 2500 pm, and more preferably a % of 1500 pm.

2. Solder joint

The solder joint is used, for example, for the connection between an IC chip and a substrate (interposer) thereof in a semiconductor package, or for the connection between a semiconductor package and a printed circuit board. In this case, the "solder joint" refers to a connection part of an electrode.

3. Method for making the solder alloy

As a method for manufacturing the brazing alloy in the present invention, the brazing alloy is made by, for example, a continuous casting method. In the continuous casting method, firstly, a raw material is supplied to a melting furnace to have a predetermined alloy composition and is heated to about 350°C to 500°C to melt the raw material.

After all the raw materials have been melted, the molten solder is continuously cast from the melting furnace into the rotary mold.

The rotary mold has, for example, a groove in the center part in the width direction of the annular plate. When the molten solder is cast, the molten solder is cast into the mold slot as the rotary mold rotates. The amount of the molten solder supplied to the mold is appropriately adjusted depending on the number of rotations of the mold and the frequency of microvibrations such as ultrasonic waves applied to the molten solder in the mold. For example, when an ultrasonic wave is applied, an ultrasonic vibration device is attached to the side surface of the rotary mold. In the present invention, the frequency of the ultrasonic wave applied to the molten solder is not particularly limited, but may be, for example, 10 kHz or more.

In the present invention, by attaching an ultrasonic device to the rotary mold and applying ultrasonic waves to the molten weld, the microstructure as described above is obtained. In the composition of the brazing alloy of the present invention, the area ratio of the intermetallic compound is not too high and a good balance with the maximum grain size is achieved. The details are not clear, but are assumed as follows. In Sn-Cu brazing alloy, SnCu compound is generated as primary crystal during solidification, and due to segregation, a part having excessively high Cu content is generated, and SnCu compound may be formed. thick. Therefore, in the present invention, the segregation of the SnCu compound is prevented by applying a microvibration such as an ultrasonic wave, and the generation of the coarse SnCu compound can be prevented.

The molten solder poured into the mold is cooled to about 150°C at a cooling rate of about 10°C/s to 50°C/s. To obtain the cooling rate, the bottom of the rotary mold is immersed in cooling water, or the cooling water is circulated in the mold using a cooler or the like.

The cooled braze alloy is guided out of the mold through the guide and cut to a predetermined length. The solder alloy reaching the guide is cooled to approximately 80°C to 200°C. In the brazing alloy of the present invention, since the intermetallic compound within the brazing alloy is fine, breakage that may occur during guide contact or the like in conventional cases can be prevented.

The solder alloy after cutting is shipped in the form of solder bar. The brazing alloy of the present invention does not break on impact during transportation.

examples

(1) Evaluation sample preparation

To demonstrate the effects of the present invention, a bar weld was prepared and tested in the following manner. The raw materials were weighed, and put into a melting furnace and melted in the melting furnace whose temperature was set at 450°C, and then the molten solder was poured into the grooves of the rotary mold in which the water circulated. . The cooling rate was approximately 30 °C/s. An ultrasonic oscillator was attached to the rotary mold, and an ultrasonic wave having an output of 5 W and 60 kHz was applied when casting the molten solder.

Next, the continuous cast product was guided from the rotary mold to the outside of the rotary mold. Next, the continuous cast product was cut to an appropriate length, and bar welds were prepared to have a total length of 10 m, including a bar weld with a width of 10 mm and a length of 300 m. mm. The evaluation method is described below.

(2) Evaluation method

(2-1) Intermetallic Compound Area Ratio (MIC)

The longitudinal central part (cross section) of the prepared bar solder was cut and an image of the composition was taken using a SEM scanning electron microscope (magnification: 250x). The image obtained was analyzed to identify an intermetallic compound. Since the intermetallic compound had a dark gray color, the intermetallic compound was determined from the color tone. The area ratio was determined as the area ratio of the intermetallic compound exhibiting dark gray to the image region. The area proportion of 20% or less was designated "oo", the area proportion of more than 20% and 40% or less was designated "O", and the area proportion of more than 40% was designated "* ". As long as the evaluation of the area ratio is "oo" or "O", there is no practical problem. In evaluation, the area of the region of the image photographed at 250x magnification could be assumed to be the cross-sectional area of the solder alloy, and the total area of the dark gray portion could be assumed to be the cross-sectional area of all intermetallic compounds.

(2-2) Maximum grain size

Among the intermetallic compounds identified from the image obtained, the largest grain size was selected with the naked eye. Two lines parallel to each other were drawn for the grains to maximize the interval, and the interval was set at the maximum grain size. The maximum grain size of 100 pm or less was designated "O", and the maximum grain size greater than 100 pm was designated "*".

(2-3) Relationship (1)

The value obtained by multiplying the results obtained from (2-1) and (2-2) of 3000 (pm % ) or less was designated "O", and the value greater than 3000 (pm %) was designated " * ”.

(2-4) Bar weld failure

With regard to the rupture of the bar weld, the bar weld from solidification to shear was observed with the naked eye. The case in which no detachment, breakage, collapse or the like occurred in the bar weld was designated "O", and the case in which slight detachment, breakage, collapse or the like occurred was designated "*".

Assuming that rupture of the bar solder occurs at room temperature during transportation, using six surfaces of the bar weld having a width of 10 mm and a length of 300 mm as evaluation surfaces, the bar weld was dropped manually freely from the height of 1 m to the concrete surface with each evaluation surface looking down (a total of six times) and the bar weld after the fall was observed with the naked eye. The “1m height” represents the height of the bar weld testing surfaces from the concrete surface. In this drop test, the case where no new spalling, cracking or the like was generated in the bar weld was designated "O", and the case where new spalling, cracking or the like was generated was designated " * ". .

The results of the evaluation are shown below.

Underlining indicates that the value is outside the scope of the present invention.

Examples 5 to 16 and 18 to 30 are examples according to the present invention.

As is evident from the results in Table 1, it was found that in any of the examples according to the present invention, the cast product could be cast continuously without the brazing alloy breaking or the like during casting. continuous casting. Additionally, even in the drop test after cooling to room temperature, no breakage of the bar solder was observed.

On the other hand, in Comparative Examples 1 and 2, since the Cu content was too high, the intermetallic compound became thick, and the breakage of the bar solder from solidification to shear was confirmed. Additionally, peeling or cracking occurred in the drop test at room temperature. In Comparative Examples 3 and 6, since ultrasonic waves were not applied to the molten solder cast in the mold, breakage was observed from solidification to shear, and new detachment or cracking was observed in the drop test at room temperature.

In Comparative Examples 4, 5 and 7, since ultrasonic waves were not applied to the molten solder cast in the mold, breakage from solidification to shear was observed, but no new detachment or cracking was observed in the drop test. room temperature, since the Cu content was relatively low. In Comparative Example 8, the precipitation amount of the coarse intermetallic compound was large, and the breakage of the bar weld from solidification to shear was confirmed. Additionally, peeling or cracking occurred in the drop test at room temperature.

Also, in Comparative Examples 1 to 8, in addition to breakage or the like, occurrence of burrs and thickness irregularities were observed in a bar weld, and a stable bar weld without burrs and a constant thickness was not made unlike the examples.

The results of SEM image observation of the cross section are shown for the examples and comparative examples shown in Table 1.

FIG. 1 is a cross-sectional image of a brazing alloy from Example 7. As seen in the image, the maximum grain size in Example 7, where ultrasonic waves were applied, was revealed to be 58.50 | jm, which is 100 jm or less. Additionally, it was revealed that the area ratio in Example 7 was 15% and that the relation (1) was satisfied.

FIG. 2 is a cross-sectional view of Example 8 and Comparative Example 4, with FIG. 2(a) the image of Example 8 and FIG. 2(b) the image of Comparative Example 4. FIG. 2(a) and FIG. 2(b) show a change in grain size depending on whether or not an ultrasonic wave is applied.

It was found that, in Example 8, the maximum grain size was 60.44 µm and the area ratio was 18.6%, and relation (1) was satisfied. In Examples 1 to 7 and Examples 9 to 29, it was confirmed in the same way that the maximum grain size was 100 μm or less and that the relation (1) was satisfied.

On the other hand, it was found that, in Comparative Example 4, since no ultrasonic wave was applied, the maximum grain size was 108.72 μm, which exceeds 100 μm, and coarse intermetallic compound was precipitated. Additionally, it was found that, in Comparative Example 4, the area ratio was 28.12% and the relation (1) was not satisfied. Similarly, it was found that in the other comparative examples the maximum grain size was greater than 100 μm and relationship (1) was not satisfied.

Claims (2)

1. A solder bar, having an alloy composition comprising, by mass % , 0.8 % to 10 % Cu, 0.03% to 0.4% Ni, optionally at least one 0.3% or less P, 0.3% or less Ge, and 0.3% or less Ga, optionally at least one selected from at least one group from a group consisting of at least one of In, Sb, Zn and Ag in a total amount of 5% or less, and a group consisting of at least one of Mn, Cr, Co, Fe, Si, Al, Ti and rare earth elements in a total amount 1% or less, the balance being Sn and including an intermetallic compound, wherein the intermetallic compound has a maximum grain size of 100 µm or less in a region at least 50 µm from a surface of the bar weld, where the intermetallic compound is mainly (Cu, Ni) ⁶ Sn ⁵ . 2. The bar weld according to claim 1, wherein the following relation (1) is satisfied: The maximum grain size (jm ) * area ratio (%) of the intermetallic compound of the brazing alloy < 3000 (jm % )....(1).